This invention relates to an optical path converter, and more particularly relates to a waveguide-type optical path converter for converting a propagation direction of light using an end face reflection technique.
Optical communication-systems and optical signal switching systems typically include an optical modulator, optical switch and optical multiplexer/separator, etc., which are optical waveguide-type devices. Recently, research on optical wiring and the like on an optical waveguide substrate has been carried out and techniques for efficient arrangement with little loss of optical waveguide-type devices are of increasing importance. Among them, an optical path converting technique for converting a propagation direction of light is important to miniaturize apparatus which use optical devices.
As an optical path conversion technique, an end face reflection technique is well known in the art. For example, this technique is disclosed in S. Valette, "State of the art of integrated technology at LETI for achieving passive optical components", Journal of Modern Optics, 1988, Vol. 35, No. 6, pp. 993-1005.
The end face reflection technique has a feature that optical path conversion efficiency is high and it has a wide range of optical path conversion. In this technique, an end face of a substrate and a waveguide is ground so that an angle between a waveguide face and the end face being ground becomes 90 degrees and so that a head of the waveguide appears on a face being ground. Next, the ground face is coated with a reflective film.
Referring to FIG. 1, a conventional waveguide-type optical path converter will be described. FIG. 1 shows a perspective view of the conventional converter.
In FIG. 1, a silicon (Si) crystal substrate 1 is covered with a cladding layer 2, in which first and second core layers 8 and 9 are formed. The cladding layer 2 and the first and second core layers constitute two optical waveguides. The first and second core layers 8 and 9 merge with each other near one side of the cladding layer 2.
An end face of a common core layer 3c is exposed by cutting the common core layer at a plane normal to the waveguides. The exposed face is ground and is covered with a reflective film 6.
In addition, the other ends 3a and 3b of the first and the second core layers appear on the opposite side of the cladding layer 2.
Since the cladding layer 2 has a lower refractive index than that of the core layers 8 and 9, light propagates mainly through the core layers.
When light is inputted through the end surface 3a of the first core layer 8, the input light propagates mainly through the first core layer 8 to the end surface 3c of the merged or common core layer. The light is reflected at the reflective film 6. The reflected light propagates through the second core layer 9 and is outputted through the end surface 3b of the second core layer. Thus, the propagation direction of the light is changed ("converted").
Although this conventional waveguide-type optical path converter has several advantages, it nevertheless has a disadvantage in that the location at which the optical path changes direction is limited to the end face of a substrate. Therefore, it is impossible to accomplish optical path conversion at positions other than ends of a substrate. Moreover, the conventional converter has another disadvantage in that its fabrication process is complex and unsuitable for mass production because of the requirement for grinding of the waveguide end face and the coating of the waveguide end face with the reflective film one device by one device.